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Florida Republican gubernatorial nominee U.S. Rep. Byron Donalds linked U.S. measles outbreaks to illegal immigration.
On CBS News’ “Face the Nation” on Aug. 23, host Margaret Brennan said Florida is below the immunization rate needed to achieve herd immunity for measles. Brennan then asked Donalds if his guidance for Florida parents would be to get their kids vaccinated.
“No,” Donalds said, “actually my message to Floridians and, quite frankly, to Americans is the reason why we have seen a measles outbreak in certain parts of the country is because of rampant illegal immigration into the United States from the previous administration.”
Donalds pointed to measles outbreaks in El Paso, Texas and southwest Florida, and said people who are in the U.S. illegally have not followed the measles, mumps and rubella vaccination schedule.
He continued, “So the key thing is, you number one, you got to control immigration into your country. You can’t have an entire segment of people, more than 10 million, coming to your country without that vaccination schedule.”
It’s inaccurate that 10 million immigrants entered the U.S. illegally during Joe Biden’s presidency, when the administration released about 4.3 million people into the U.S. to await immigration court hearings.
And there’s no evidence linking measles outbreaks to immigrants in the U.S. Infectious disease experts told PolitiFact that a decline in measles, mumps and rubella vaccinations in the U.S. is the primary driver of the outbreaks. Around 94% of confirmed cases in 2026 are in people who are unvaccinated or whose vaccination status is unknown.
Donalds’ campaign did not respond to a request for information to support his statement.
Similar claims about immigrants circulated during measles outbreaks years before Biden’s administration.
George Rust, a Florida State University College of Medicine professor and epidemiologist, said the U.S. for decades had sporadic measles cases that typically started after U.S. travelers caught the virus overseas and experienced symptoms after returning home.
“Maybe one or two additional individuals would catch it from them, but because of high immunization rates and rapid public health response, there would be no second wave of cases,” Rust said. “Now, we are seeing more outbreaks because that same scenario plays out in the context of clusters of people who are unvaccinated, which allows for greater spread.”
What’s the status of measles in the U.S.?
The ongoing 2026 measles outbreak has surpassed 2025’s record-breaking case numbers, which were the most since 1991.
Measles is a highly contagious respiratory virus. Infection can lead to severe complications such as pneumonia, brain swelling and death. In 2025, two children and one adult died from measles, the first U.S. fatalities attributed to the virus in more than a decade. On Aug. 25, Pennsylvania’s health department said two more unvaccinated people, whose ages were not made public, died from the virus.
Receiving the recommended two doses of the MMR vaccine is 97% effective against infection.
“Ninety percent of unvaccinated people who are exposed are likely to catch it,” Rust said. “Because of the high rate of infectivity, measles outbreaks can spread exponentially in segments of the population that are unimmunized or not immune.”
Is measles spread by immigrants?
The CDC does not report the immigration status of people infected with measles in the U.S., making it impossible to definitively tie any measles outbreaks to immigrants in the country illegally. Contact tracing during past outbreaks has shown that measles typically enters the U.S. from unvaccinated residents who traveled internationally, mostly to Europe and the Western Pacific region.
The U.S. achieved measles elimination status in 2000, which means the virus stopped continuously spreading domestically.
“Any given chain begins with someone who traveled,” said Dr. Paul Spiegel, distinguished professor of the practice and director at Johns Hopkins Center for Humanitarian Health. “An introduction becomes an outbreak only when the virus reaches enough susceptible, unvaccinated people, and the importation data do not point to migrants in any case.”
Dr. William Schaffner, a Vanderbilt Health infectious diseases specialist, agreed, saying “the very substantial majority” of cases are “caused by our own unvaccinated children who go abroad, pick up the measles and then bring it back home.” Only a minority of cases, he said, are caused by foreigners coming to the U.S.
Measles outbreaks on the U.S. west coast often come from unvaccinated U.S. residents returning from Asia, experts said, while east and central U.S. outbreaks typically originate from U.S. residents returning from Europe. “I have never seen data indicating that notable introductions have come from south of the border,” Schaffner said.
In El Paso, Texas, a measles outbreak in early 2026 occurred among immigrants in an Immigration and Customs Enforcement detention facility and a nearby federal detention facility that houses both migrants and U.S. citizens. Public health officials attributed the spread to the facilities’ poor conditions and a lack of federal data on inmates’ vaccination statuses. It’s unclear when any of the infected immigrants entered the U.S. ICE detains many people who are not recent arrivals.
In Southwest Florida, where Donalds lives, Florida’s largest outbreak was centered on Ave Maria University in Collier County. The university, citing the state health department’s contact tracing, said it most likely began with a student’s out-of-state holiday travel.
Some of the largest outbreaks this year were in areas with large Amish and Mennonite communities that typically have lower vaccination rates. Past outbreaks also clustered in similar, vaccine-averse communities.
MMR vaccination in other countries
Countries where many immigrants in the U.S. illegally come from, such as Mexico, Guatemala and Honduras, all include the MMR vaccine in their routine childhood schedules.
Experts said the problem is not that these countries lack vaccination programs, but that many have seen vaccine coverage slip below the 95% threshold needed to stop measles transmission — the same problem the U.S. has.
This year, El Salvador and Honduras have reported small numbers of measles cases. Guatemala and Mexico are dealing with large outbreaks, with the vast majority of cases occurring in unvaccinated people.
Mexico’s measles epidemic, however, originated in the U.S., not the other way around. The country’s outbreak began in Chihuahua, Mexico, in February 2025, and was traced to an unvaccinated nine-year-old from a Mennonite community who was infected while visiting relatives in Seminole, Texas, as the state’s outbreak was taking off.
“Discussions of migration and infectious disease often get the causal relationship backward,” Spiegel said. “Human mobility of every kind — tourism, business travel, migration — can move a virus from one place to another, but movement does not by itself create an outbreak; susceptibility does.”
Our ruling
Donalds said “rampant illegal immigration” during the Biden administration is the cause of “a measles outbreak in certain parts of the country.”
Measles is typically introduced by U.S. travelers returning from international travel. Experts said a U.S. decline in MMR vaccinations is the primary driver of the outbreak.
We found no data pointing to immigrants who entered the country illegally as the reason for any outbreak. Top countries of origin for immigrants in the U.S. illegally also include the MMR vaccine in their routine childhood schedules.
The burden of proof is on the speaker, and Donalds provided no evidence to support his statement. We rate it False.
Our sources
- CBS News, Transcript: Rep. Byron Donalds on “Face the Nation with Margaret Brennan,” Aug. 23, 2026, Aug. 23, 2026
- U.S. Centers for Disease Control and Prevention, Measles Cases and Outbreaks, Updated Aug. 21, 2026
- U.S. Centers for Disease Control and Prevention, About Global Measles, July 14, 2025
- U.S. Centers for Disease Control and Prevention, History of Measles, April 29, 2026
- U.S. Centers for Disease Control and Prevention, Chapter 7: Measles, Updated June 3, 2025
- ABC News, 2 people die from measles in Pennsylvania, marking state’s first deaths in 35 years, Aug. 25, 2026
- University of Michigan Center for Infectious Disease Research and Policy CDC adds 211 new cases to accelerating US measles outbreak, Aug. 21, 2026
- USdiseasetracker.org, Tracking Measles, Accessed Aug. 25, 2026
- PolitiFact, Ask PolitiFact: Is Texas measles outbreak linked to ‘border’? No evidence, officials say, March 7, 2025
- PolitiFact, No, illegal immigrants and refugees are not causing six eradicated diseases to come back, June 10, 2019
- PolitiFact, Rush Limbaugh blames measles outbreak on immigrant children, Feb. 5, 2015
- PolitiFact, A parent’s guide to measles: What to look for and how to prevent infection, Jan. 30, 2026
- Forbes, A Doctor Fact-Checks Dr. Oz And Byron Donalds Comments On ‘Face The Nation’, Aug. 24, 2026
- NBC News, Measles outbreak linked to a Florida university as cases keep rising in the U.S., Feb. 3, 2026
- CBS News Miami, Florida pediatricians push back against Trump’s vaccine order, saying it will worsen measles outbreak in the state, Aug. 11, 2026
- KFF, Kindergarten Routine Vaccination Rates Continue to Decline, Aug. 21, 2026
- Central Florida Public Media, Florida’s measles cases continue to rise, March 5, 2026
- Stanford Medicine, Measles in America: Five things to know from a Stanford Medicine expert, Jan. 28, 2026
- Johns Hopkins Whiting School of Engineering, What’s behind the measles blast-from-the-past? Lauren Gardner’s team combines data-driven engineering and social science methods to understand drivers of the largest measles outbreak in 30 years, June 25, 2026
- Johns Hopkins Bloomberg School of Public Health, Childhood Immunization Status Florida, Updated Aug. 25, 2026
- FactCheck.org, Measles Misinformation Gets an Immigration Twist, April 26, 2019
- The Guardian, US measles outbreak not linked to illegal immigration, health official says, Feb. 23, 2015
- WHO Pan American Health Organization, Immunization coverage throughout the life course in the Americas, Accessed Aug. 25, 2026
- WHO Pan American Health Organization, Vaccination schedules map, Accessed Aug. 25, 2026
- Email interview, George Rust, professor and epidemiologist at Florida State University College of Medicine, Aug. 24, 2026
- Phone interview, Dr. William Schaffner, professor of infectious diseases at Vanderbilt Health, Aug. 25, 2026
- Email interview, Dr. Paul Spiegel, distinguished professor of the practice and director at Johns Hopkins Center for Humanitarian Health, Aug. 25, 2026
